In an electronic flash device suitable for use with a zoom lens camera, it was proposed to place a flash tube such as a xenon discharge flash tube in a lamp holder which is disposed in a housing so as to be moveable in the fore and aft direction. As the fore and aft movement of the lamp holder causes the distance between the flash tube and a fresnel lens placed in front of the lamp holder to change, the beam angle (or the cone angle) of the flash light that is produced from the electronic flash device changes. The movement of the lamp holder may be coordinated with the movement of the zoom lens of the camera such that the beam angle of the flash light corresponds to the field of view of the camera. See JP2003-84340.
As the lamp holders for the conventional electronic flash devices are typically made of plastic material such as polyacrylate, the repeated lighting of the flash tube could cause thermal damage (such as permanent deformation) to the lamp holder although the duration of each light emission is extremely short if the flash tube is lighted at a high frequency for a prolonged period of time. Therefore, conventionally, powerful electronic flash devices are sometimes provided with a protection circuit for limiting the repeated lighting of the flash tube within a prescribed number of times during a prescribed period of time. However, this is found to be highly inconvenient for professional cameramen who require continuous use of the electronic flash device for a prolonged period of time.
In particular, when a metallic concave mirror provided on the lamp holder is contemplated to be used as a trigger electrode for the xenon discharge flash tube and is therefore brought into contact with the xenon flash tube, the heat conduction from the flash tube to the metallic concave mirror or the lamp holder will be so intense that the risk of thermally damaging the lamp holder increases.